Cellulitis vs erysipelas
Formal Definition
Two related but distinct superficial bacterial skin infections: cellulitis involves the deeper dermis and subcutaneous fat (ill-defined borders, often with skin marking changes from lymphedema/dependent edema); erysipelas involves the more superficial dermis and lymphatics with classic sharply demarcated, raised, erythematous borders (often with intense lymphangitis streaking proximally); both are typically caused by Streptococcus pyogenes (Group A Strep) or Staphylococcus aureus, but erysipelas is almost exclusively streptococcal; both treated with empiric antibiotics covering streptococci and staphylococci, often with elevated limb, and sometimes with compression for chronic lymphedema.
How It's Used on the Ward
"Cellulitis" vs "erysipelas" — two flavors of skin infection seen frequently on the wards; cellulitis has fuzzy borders and is the deeper skin infection, erysipelas has a sharp raised border (you can draw a line with a pen and it stays inside) and is more superficial; you'll see both often in patients with chronic lymphedema or venous stasis disease coming in for IV antibiotics.
Example
""58-year-old man with chronic lower extremity lymphedema from prior DVT presents with 2 days of progressive left lower leg erythema, warmth, swelling. Exam: sharply demarcated raised erythematous border extending from ankle to mid-calf, intensely tender, no fluctuance, no crepitus, no drainage, no systemic toxicity. Diagnosis: erysipelas (vs cellulitis) in setting of chronic lymphedema. Admitted for IV penicillin G (covers strep — most common cause of erysipelas) plus amoxicillin-clavulanate until cultures, leg elevation. Discharged on oral penicillin VK to complete 10-day course.""
Clinical Context
Cellulitis: deeper dermis + subcutaneous fat, ill-defined borders, most common cause = Strep pyogenes or Staph aureus (including MRSA — consider if purulent or post-traumatic). Treatment: empiric coverage with cephalexin / dicloxacillin (MSSA), trimethoprim-sulfamethoxazole or doxycycline if MRSA-risk (purulent, post-traumatic, prior MRSA, IVDU). Severe: vancomycin + cefepime. Erysipelas: superficial dermis and lymphatics, sharply demarcated raised border, almost exclusively Strep pyogenes. Treatment: penicillin (drug of choice), amoxicillin, or cephalexin. Coverage for Staph not needed unless atypical features. Elevation, warm compresses initially for lymphatic drainage, compression after acute phase to address underlying lymphedema. Distinguishing from DVT: cellulitis typically more diffuse, well-circumscribed erythema, warmth; DVT typically unilateral swelling + calf tenderness without significant skin changes. Mimics: venous stasis dermatitis (bilateral, no fever, chronic), contact dermatitis (exposure history), necrotizing fasciitis (severe pain out of proportion, systemic toxicity, crepitus — surgical emergency), DVT (use Wells criteria + duplex US if uncertain). Recurrent cellulitis in chronic lymphedema: chronic suppressive penicillin, weight management, skin care.